90 xj engine stutter

Ok, you guys have bailed me out in the past when Ive come here after beating my head against the garage door for a while, so Im counting on you all again .....

90 xj 4.0 automatic a.k.a. The Wifes Beast

Prelude to the tale-
Had it smopgged a week ago and it sat in the driveway till I got back from the DMV (felt like I was there a week too) Tagged the plates and went to take it for a drive, started fine, had good acceleration for about 50 feet, then it started to stumble, the more gas i gave it, the more it wanted to die, which it eventually did halfway back home. pulled it in the driveway and checked the first thing that came to my mind, fuel filter, its fairly new but I pulled it anyway, blew thru it no prob and could still see light thru it, put it back on. I checked the egr valve and solenoid per the vaccume tests and they seem ok, now sitting with it idling, it will be fine for a while, then start sucking air thru the intake like mad and idle will drop to almost nothing, then it will rev to about 2k for a sec and even out, I have the air filter out by the way suspecting it. It seems like a vaccume leak to me, or maybe a bad fuel pump, the longer I looked into it, the harder it got to start too, any ideas ?????? Its driving me nutty .....

OK - first things off the top of my head.

1) Check the wiring from the CPS. I had something like this happen last week, and it turned out that the CPS harness had melted thru, and engine vibrations were tapping the bare wires on the exhaust and shorting it out intermittently (I HATE intermittent faults - so difficult to track...)

2) The most common vacuum leak I see on ANY inline six cylinder engine (with an aluminum manifold) is usually in the centre of the intake. Reason? Aluminum expands faster than Iron, and this will cause bolts to work loose. This one can be located as it usually goes away when the engine is warm, but not always. Check the torque on the manifold bolts, and use LocTite 272 when you put them back in. I also suggest the use of brass nuts on the end studs on the exhaust, if your local carries them, as brass does not sieze on steel when heated (which is why I use brass or bronze hardware on all my exhaust.)

For further diagnosis, more information is required...

5-90

Another thing I noticed messing with it, if I sit there and hold the idle up to about 2k, it will stay there with no stutter, its only at idle and in gear thats its acting up, that help anybody at all ???


CPS looks great btw, I ran into that problem a few months back and now have the harness tied up along the firewall. Thanks for the reply !

OK - that's got me a little more inclined to think "vacuum leak" - in my experience, you only really notice those at idle. The quick and dirty way to check is to get a can of carburettor cleaner and fog the engine bay around the vacuum lines. You should get an increase in RPM and you will see the cloud disappear when you fog the area with the leak.

I would think that checking maifold bolt torque is good PM, tho, from what I've seen of inline sixes...

5-90

5-90 gave some good advice, have found the same problems on my XJ´s.
A couple of other, good checks, are the temp. sensor, 02 sensor and knock sensor harness where it continues from the front end of the fuel rail harness. It often flops over on the exhaust manifold or rubs someplace.
Look at the rod in the EGR while blipping the throttle, most times there is some movement, you can see if it´s seating. Make sure it´s seated (even if you have to use a pair of needle nose pliers tro do it) unplug and block the vacume line to the EGR. Give it a test drive.
Look in the distributor cap. Check the cap connections for corrosion. Move the high voltage wires around (reroute a little) see if there is a change.
I periodically check and run my fingers across the bottom of most all the vacum lines, often find a rub or scuff, occasioanally it´s worn through. Look at the MAP vacume plug on the back of the throttle body, and at the MAP. Check the regulator, vacume line real close.
Been there done that, good news is, there usually is a solution.

Lots of good ideas, some I have checked already, but am going to check again, you never know. The one thing that really has me wondering tho, is why I get an almost imediate stall when I pop it into gear, as soon as the trans is engaged, death. Ill keep following vac lines, altho I replaced 90% of them last year and rerouted them off the block and manifold. Thanks for the info guys, any other ideas, please post em.

Interesting update

Ok, I disconnected the vac line from the MAP sensor...and it will actually drive without stalling, the idle still fluctuates a little, and I still get a pop out of the air cleaner intake hose every few minutes, but it drives, think that means the map is bad ???? I dont seem to see a diff in driveability with the MAP vac hose plugged or open, just as long as its disconnected from the MAP....

Have you tried...

Howdy. Just wanted to ask, I know on my '91 I can get the codes from the computer fairly easily (don't start engine, but on, off, on, off, on, then read the flashes on the "check engine" light). Flashes of 5 and 5 is the end of file and no problem found. Can your '90 give codes? In other words, what does the computer think the problem is?

Just my $0.02 worth from a lifetime owner.

OK my line of thought, problem stalling. Some causes.
High idle not working, temp. sender (harness)
Faulty or malf in EGR. EGR (sticking), temp. sender, EGR solenoid,TPS, knock sensor (harness)
Vacume leak, will often make it hunt, high idle, then the sensors (02) overcorrect and stall or near stall.
Just had smog test, many inspectors/testers like to pull vacume lines, as a function test for various sensors (EGR etc.) as part of the visual inspection. Problem just started, something loose and fell off.
High voltage leak, coil wire etc. messes with idle, sometimes smooths out at moderate RPM, will usually break down again at higher RPM´s. Bucking and stalling sometimes at low RPM.
Unplugging the MAP? You´ll have to ask somebody with more knowledge of the Jeep sensor loop and the interrelations, than me (I unplugged, the electrical, on my MAP, the other day, with the motor running, stopped dead). I unplugged my sync generator (distributor) the other day, trying to find a rough idle, and it started idleing really nice. Heck if I know. Many interrelationships between sensors, I suspect a sensor, but which one? Time to break out the old ohm meter.
Gummed up idle motor, time to clean the throttle body, also control by the same sensors as the EGR.
Faulty or failing fuel regulator, usually mess up at higher RPM´s not low.
Most any time, I´ve had a stalling problem it was the EGR , moisture in a connector (ignition or sensor), or an unplugged or leaking vacume line.
I guess I´ve been lucky, all of the CPS sensors I´ve seen fail, failed completely. No intermittant or partial problems.

Maybe 5-90, Nick or Eagle can jump in and share some computer/sensor knowledge.

I'll chew on this one some more, but...

I've never seen an intermittent CPS failure that was caused AT THE SENSOR - but you can get the melted insulation that makes it looks like an intermittent CPS failure. Either way, the solution is the same - replace the thing (OEMR, $40 or so.) If there's an aftermarket source for these, I want to know about it! NOTE - the 87-90 and 91-up units are different, and even the OEMR catalogue lists different numbers for 87-88 and 89-90.

As far as codes, there aren't any on the 90. The only data from the Renix computer is realtime drive data, which is only readable with the Snap-on MT2500 or the DRBII scan tool. There are no stored codes, therefore no way to access them.

Most other sensors would cause rich/lean fuel conditions, but you would still run in "limp home" mode. What were your smog results like? Anything useful there?

5-90

update

Thanks for the posts guys, I just replaced the MAP and same deal, idles like crap for a bit, then dies, manually pulling the throttle lever to about 2k, runs great, no misses or stalls, put it in gear, it dies. occasionally at idle, it will drop real low to the point of death, then start sucking in air thru the air cleaner intake hose, jump up to about 2k for a sec, then smooth out and start all over. Disconnect the vac line to the MAP and I can actually drive it without it stalling, altho I can hear it pop out of the air cleaner box ever so often. As for the recent smog, It had very high NoX reading at first, (280?) I tuned it up, filled it with new gas, ran a cleaner thru the fuel system, drove it for the weekend, then on Monday it was down to 170, still too high. They changed ECM Temp sensor, and O2 Sensor, passed with an 83 NoX reading. Drove it home, it sat a week, then WHAM....... It actually driving with the vac line from the MAP disconnected has me thinking maybe its something with the Throttle Body, but all of a sudden with no warning ??? Ill take it off tomorrow and clean it out. I appreciate the posts guys, if you think of anything else, throw it at me....

Oh BTW

Forgot to mention, I very recently replaced the CPS, the harness is routed up along the fire wall and out of harms way. At the same time I ran all new Vac lines and routed them away from heat as well, no vac lines or wire harnesses look damaged at all..

My problem was similiar on my "88. Found a cracked distributer cap, changed it out. Everything fine. Another time, idle was erratic and A used AIS solved that! Good luck

That surging, to 2000 and then dieing, makes me lean towards, 5-90 theory of a vacume leak and/or the EGR is passing recirculated exhaust gases at the wrong times. Something to mess up the values at the 02 sensor and maybe a conflict between the 02 sensor and the throttle position sensor.
Just a wild thought, was the gas additive you put in there 02 and/or cat, compatable? Another wild thought, I sometimes drive in third world countries, they like to water there gas sometimes, really makes things run like &&%)?, I´ve gotten so I carry a can or two of gas tank dryer with me (02 and cat. compatable).
Like dusterboy, mentioned, high voltage ignition issues and or moisture, will mess with your idle and cause stalling. Also cross fire will give you that, intake backfire. Sometimes will smooth out at middle RPM´s, but will start breaking up bad again above 3500 or so.
Good luck, I seem to play the same game a couple times a year. Usually muddle through and find an explanation.
I just cleaned and added star washers to the firewall ground, really made a difference in many things, from charging, to idle and top RPM. Didn´t cure everything but sure helped.

TPS connector? 1. runs like cr*p, 2. Zooms to 2k idle

I've seen and live with these symptoms on my '90 - too lazy to clean mine, yet, as has been suggested -

Joplinray! Sorry the '90's don't run OBD like you lucky '91's, we were the last of the Renix. So no codes - but we do have interesting dents on the inside of our garage doors - about head high . . .

TPS, Hmmm....Gonna disasemble the Throttle Body and clean it all out, Ill look at the TPS while Im there. Still stuck on the fact that with the MAP Vaccume disconed it drives, albeit like crap, but it drives. Thanks for all the help guys, Im sure Ill figure it out sooner or...well, soon, the wife wants her Jeep back

Ok, all of you who first thought Intake Mani gasket leak may have been right. I fogged the engine and got no change in rpm at all, but after 3 days I figured I would pull the intake mani and have a closer look......wellllll all but 2 of the bolts, the lower middle two, were either hand tight or actually backed off a little, unbelievable .... picking up a new gasket tomorrow and Ill let you know how it goes. Thanks again for all the knowledge

I would suggest a THIN layer of RTV Copper on both sides of the new gasket, and use brass or silicon bronze bolts if you can get them quick enough (they're all threaded 3/8"-16, and I know Fastenal carries silicon bronze bolts.) Make sure to reuse the Belleville washers on reinstall, and also be sure to apply LocTite #272 to all bolts during assembly (it's the only one that will work - everything else breaks down in the heat!)

Did that last year, and no problems since...

5-90

Well, new intake mani gasket in and same crap, its going to the garage that smogged it tomorrow, thanks for all the input .

Have you carefully checked the EGR system?
I had lousy idle and very poor vacuum on our '90. It took me about 6 months to figure it out. Ended up replacing the EGR solenoid and the modulator.
Try disconnecting and plugging the vacuum feed to the EGR solenoid to see if anything changes.